Surviving the Extremes: A Doctor's Journey to the Limits of Human Endurance (20 page)

Shipwreck survivors have won their battle with the ocean, and their prize is the chance to resume their more protected lives. The abilities and the intensity that they called forth to allow them to stay
alive on the high seas are largely withdrawn—superfluous in a society where the survival instinct is not critical to survival. They resume or take on roles as fathers, mothers, and friends, and work as anything from sailors to storekeepers. In short, they become nearly indistinguishable from the rest of the population who were never put to the test. They have proven they have the qualities for survival, but most of us will never have the chance to look for those qualities in ourselves.

For a survival epic to become a story, someone has to live to tell it. People can be lucky, like the French couple in the Mediterranean, or unlucky, like some of the students on board the
Albatross.
They can survive on sheer will like Poon Lim or on raw animal instincts like the whalers on the
Essex.
But the harsher the conditions and the longer the isolation, the stricter the selection becomes. The circle of survivors tightens and then disappears as bodies and minds are pushed to their limits and beyond. We only know the stories of the winners. The greatest battles against the sea are likely to be the ones that ended in defeat, and thus their stories will never be told.

ON THE FOURTH DAY OF AN ULTRA-MARATHDN
through the Sahara Desert, Mauro Prosperi got lost. He survived a sandstorm, then with only a finger’s breadth of water in his canteen, crossed 130 miles of dunes over nine days, in temperatures above 100°F, before being rescued by an eight-year-old Tuareg girl. He is either the most incredible example of desert survival ever or the most elaborate fraud in the history of endurance sports. Can a human body, even one belonging to a superbly trained athlete, survive nine days in an oven?

The Marathon des Sables is an annual 160-mile race through the dry ocean of the Moroccan desert. Competitors are immersed in superheated air that flows over their skin and fills their lungs, bathing them in heat outside and in. They run over waves of sand—a thick, dry fluid that splashes up as each footstep sinks below the surface. Overhead is a nuclear reactor, the sun, that beams radiation through an atmosphere too thin and transparent to protect the trespassers crossing underneath.

There were 137 trespassers in the 1994 race, each one carrying his own portable microenvironment to defend his body against the surroundings. Except for water stations at the checkpoints, the racers traversed the desert self-contained, with food, spare clothing, a sleeping bag, and emergency supplies in their backpacks. They were competing against the other athletes but, even more, they were competing against the desert.

Deserts form in those parts of the earth that receive less than 10 inches of rainfall a year. About one-fifth of the world’s land surface qualifies, usually because it lies on the far side of a mountain range tall enough to create a barrier to the moisture-laden air that collects over oceans. The Sahara is the largest desert in the world, covering half of Africa, with a total area roughly equal in size to the continental United States. The Atlas Mountains along Africa’s western coast block airflow from the Atlantic. Ocean winds push the air against the mountains, and as it rises, the air cools. Because cold air cannot hold as much water as warm air, the water drips out as rain or snow, so that by the time the air has made it across the peaks and slid down the other side it has effectively been dried out. With no clouds and no moisture to absorb, deflect, or diffuse the sun’s rays, solar energy strikes the ground at full intensity, overheating the air and baking the land into sand.

Wind is created when heated surface air rises and surrounding air moves sideways along the ground to replace it. Most deserts, being open expanses, allow the wind to travel great distances in one direction at a steady speed, rolling sand along to form dunes, which can sometimes grow to be 1,000 feet high and 15 miles long. Coaxed along by the wind, dunes advance in orderly patterns, like waves. But where air heats up unevenly, hot pockets form that rise suddenly, like hot-air balloons. The strong wind sweeps up and around these pockets, pulling sand grains into its vortex, and the combination becomes a sandstorm.

At 20 miles into that day’s 50-mile run—the fourth and longest leg of the marathon—Mauro Prosperi was maintaining a good pace, so good that by early afternoon he was in seventh place. But he was about to face a much tougher array of opponents. The temperature had reached 115°F. The superheated air was stirring up swirling winds. Suddenly, Prosperi was enveloped by a sandstorm so violent that, unbeknownst to him, race officials suspended the day’s run. Despite the incredibly poor visibility, Prosperi thought he could still see the trail. He kept on running.

Windblown grains of sand pierced his skin like needles, causing his nose to bleed and cutting the inside of his throat. His competitive
spirit could not keep up with the increasing ferocity of the storm. Finally he stopped, crawled into a bush, and wrapped a towel around his face. All day the wind whipped the dunes into a raging ocean, forcing Prosperi to change locations several times lest he be swamped by a wave of sand. Eventually, night fell. By morning the sandstorm was over.

When Prosperi opened his eyes he saw only sand in every direction. What had been a competition among athletes was now a contest against nature. His goal was no longer to win the race, but to stay alive.

The Sahara desert is not obviously compatible with human life. Daytime temperatures routinely soar above 100°F; nighttime temperatures can fall well below freezing. To the untrained eye, food is scarce, water nonexistent. Few features rise above the sand, offering little chance for shelter and little aid to navigation. The Tuareg people of western and central Sahara, through evolutionary adaptation and generations of accumulated wisdom, manage to survive here, scattered as nomads wringing subsistence from the desert. But Prosperi was a crowd-control policeman from Italy, and this was his first time in the desert.

It was also the first time in the desert for the Hughes family. On vacation from England, Andrew and Jane Hughes and their preadolescent sons, Matthew and Sam, on their trip to Tunisia in 1989, became bored hanging around the hotel pool. They decided to rent a car and drive to the southern market town of Duse, at the edge of the Sahara. Thanks to bad maps and few signposts along a barely discernible road, they were soon lost and stuck in the sand. Believing they were close to Duse they got out of the car to go the rest of the way on foot. After an hour of walking with no town in sight, Andrew told Jane and the boys to return to the car and wait. He would get help and come back for them. Jane and her sons set off under a ferocious sun, carrying a liter and a half of water. They weren’t much worried; earlier they had passed some big water tanks. Andrew walked on by himself.

Humans are designed to endure heat far better than cold, but no one can withstand prolonged exposure to a blazing sun and no one can live long without water. The desert, however, offers ample opportunity for lost travelers to try to survive both. Humans must fiercely protect their internal temperature, for it holds the key to all their life functions. The human body is a mass of millions of exquisitely sequenced chemical reactions, which speed up as temperature rises. Individual changes in the cadence of those reactions will quickly lead to internal chaos, like a symphony orchestra with each member playing at a different tempo. The timing, and thus the temperature, of these reactions is so critical that if body temperature varies by more than 4°F from 98.6°F, systems begin to malfunction and the body’s formidable defenses start to crumble.

Years ago, when survival was first being examined from a scientific point of view, it was assumed, reasonably enough, that people who had adapted to desert life would have higher body temperatures than those adapted to places like the Arctic. In fact, regardless of where we live or for how many generations, all people guard the same internal temperature. We have indeed adapted to our respective environments, but we have done it by modifying our body systems and our behavior.

Heat enters or leaves an object in three ways. Where there is direct contact between two objects, heat flows from the warmer one to the cooler one—such as from sand dunes to hiking boots or from hot air to clothes—via conduction. Convection, the second form, is a kind of facilitated conduction that occurs when air circulates over one of the contact surfaces, spreading the heat faster. This is why a heater with a fan makes a room warmer faster than an oven with its door open—and why desert winds very quickly increase the temperature of human skin. The third form of heat transfer is radiation. What we experience as heat is actually the vibration of molecules. The faster something vibrates, the higher its temperature and the more energy it gives off. The sun, whose surface temperature is about 11,000°F, releases vast amounts of energy in the form of waves, which radiate through space until they collide with something, such as a human being. This in turn speeds up the molecular vibrations within that human. These sped-up vibrations are what we sense as “getting hotter.”
In the desert, direct solar energy accounts for about two-thirds of the heat load absorbed by the body.

Proteins, whether contained within eggshells or skulls, congeal at temperatures above 112°F; desert temperatures routinely surpass 120°F (temperatures in saunas can rise to over 180°F), yet brains don’t become hard-boiled at these temperatures. And heat doesn’t come only from the outside. Because no biochemical reactions are 100 percent efficient, they all give off some heat as a by-product. The busiest organs, the brain, heart, lungs, liver, and muscles, generate the most. The heat is transferred to the blood (by conduction) and then circulated through the body (convection) to maintain what we call
body temperature.

In temperate climates, air temperature is generally lower than body temperature, and as a result, body heat is constantly being given off into the space around it (radiation). The rate of heat loss depends upon the temperature differential between the environment and the body. When the air is 16°F cooler than the body, the rate of heat production is exactly offset by the rate of heat loss. This means that the human body will be in optimum heat balance when the outside temperature is 82°F. That’s the average temperature on the African plains; one solid piece of evidence that human life evolved there.

The temperature balance of 82°F applies only to a body at rest, emitting the baseline heat level called the
basal metabolic rate.
As soon as we start exercising, the metabolic rate—and consequent heat production—increases enormously. Unless the heat can be quickly dissipated, one hour of intensive exercise will raise body temperature to 140°F. Even on the temperate African plains, a man who evades a lion or captures an antelope still requires an effective way to rid his system of excess heat if he is to survive there.

So too do Italian marathon runners and British tourists lost in the desert. Temperature regulation is critically important for all humans, yet, strangely, we have no systems designed specifically to cool our bodies down, other than sweat glands, which are actually highly modified hair follicles. Thermostatic control depends on organs and tissues from other systems. The body recruits blood vessels, skin, fat, muscles,
and most important of all, because of its ability to modify conscious behavior, the brain.

To coordinate an effective response, the body must first gauge the outside temperature, so that it can begin to respond long before its core temperature becomes affected. The entire outer surface of the body is supplied with nerve endings called thermoreceptors, thermometers sensitive either to hot or to cold. Heat receptors fire more frequently as temperature rises; cold receptors fire more when temperature falls. The receptors are fine-tuned to 82°F—the optimal outside temperature for body chemistry.

Signals from the thermoreceptors are transmitted to the hypothalamus, the brain’s maintenance center, located at the base of the skull. The front of the hypothalamus contains the body’s thermostat, actively monitoring internal body temperature while also remaining exquisitely sensitive to skin temperature, its vital early-warning system. When the hypothalamus starts receiving increased signals from the heat receptors, it takes control of blood vessels and sweat glands and adjusts their function to facilitate cooling. Without the alarm set off by changes in skin temperature, the hypothalamus would be unable to react to an increase in core body temperature until after it occurred. This would be highly dangerous, given that a 4°F differential is enough to disrupt the body’s functions. Should the thermostat in the hypothalamus itself become disrupted, the entire thermoregulatory system would rapidly spin out of control.

Our body’s margin of survival is precariously thin. We spend our entire lives less than 10°F away from fatal overheating, a frightening thought on a planet where temperatures can vary by more than 100°F. Clearly, our bodies need a reliable cooling system.